Means for minimizing wear of internal external gear pumps



Feb. 8, 1955 w. E. BAKEWELL 2,701,532

MEANS FOR MINIMIZING WEAR OF INTERNAL EXTERNAL GEAR PUMPS Filed May 8,1952 2' Sheets-Sheet l Feb. 8, 1955 w. E. BAKEWELL 2,701,532

MEANS FOR MINIMIZING WEAR OF INTERNAL EXTERNAL GEAR PUMPS Fild May 8.1952 2 Sheets-Sheet 2 United States Patent MEANS FOR NHNIMIZING WEAR OFINTERNAL EXTERNAL GEAR PUMPS William E. Bakewell, Cedar Falls, IowaApplication May 8, 1952, Serial No. 286,771

2. Claims. (Cl. 103-126) My invention relates to the art of internalexternal type gear pumps and specifically is a means for reducing lossof pumping efiiciency resulting from canting the gears in pumps of thistype. This application is a continuation in part of my abandonedapplication Serial Number 738,183, filed March 29, 1947.

Internal external gear pumps, hereafter abbreviated to I. E. G. pumps,have been known and used for a long time. They are eflicient units,particularly for high pressure work, as long as they are operating asintended. Whenever the sliding fit between the external gear and thecase is such as to cause leakage from the front to the back of theexternal gear, however, the conventional I. E. G. pump deterioratesrapidly. The rate of wear increases enormously and in a short time afterleakage has once started, the pump is incapable of producing its normaloperating pressures easily and perhaps not at all.

In the conventional I. E. G. pump the external gear is supposed toexclude all liquid moved by the pump from the area behind it bymaintaining a sliding fit seal between its rear periphery and thehousing. Thus the pressure behind the gear is the same on both sidesunder optimum operating conditions for the conventional I. E. G. pump.On the front face of the external gear, however, we have widelydiffering pressures on its two halves. On one half of the external gearare intake pressures and on the other outlet pressures. If this were notso the pump would not be accomplishing anything. Consequently in theoptimum situation for the conventional I. E. G. pump, we have forcesexerted tending to cant the external gear. Outlet pressures workingagainst the common pressure behind the external gear creates onepressure diiferential. The inlet pressures working against commonpressure behind the external gear produces a different pressuredifferential. As outlet pressures are greater than inlet pressures, theexternal gear tends to be forced rearwardly on the pressure side; andbecause it is rigid, it naturally moves forward at the other side. Themovement just described is accentuated if the pump is subject to loadsuddenly. Even if the system in which the pump is used is equipped witha pressure relief valve, sudden loads can cause momentary peak loads farin excess of the value at which the relief valve is set. The forceapplied tending to cant the external gear, therefore, can be very greatat times. In fact, a sudden force applied in this manner will causegreater movement than would the same force applied with graduallyincreasing force, as there is an impact force applied as a result of thevelocity of liquid being pumped before the load is applied.

Any canting of the external gear tends to alter tolerances at the pointwhere the rear periphery of the external gear and the housing aresupposed to maintain a sliding seal. As these tolerances must bemaintained within close limits to avoid leakage, canting of the externalgear will usually cause some leakage. Also once leakage has started, itwill usually get more pronounced as time goes by. Whether the leak thatoccurs vents the rear of the external gear to inlet or outlet pressuresmakes little difference to the final outcome as to pump operation. Ifthe entire rear of the external gear is subjected to outlet pressures,the external gear tends to be moved toward the front of the gear casewith resulting undesirable wear. Likewise undesirable wear is the resultif the entire rear of the external gear has only inlet pressures appliedthe gear tends to be moved to the rear of the pump housing, because thetotal pressure at the rear of gear will be less than the combined inletand outlet pressures exerted on the face. Either of these motions causesgreat pressures to be exerted on the shaft bearings. In fact to resistthese pressures specially designed and relatively expensive bearingsmust be used. The expense of these bearings makes the cost of the pumpvery high and in some cases prohibitive. Failure to use these specialbearings results in frequent pump failure which is also undesirable.Obviously the user of the conventional gear type pump is faced with adilemma. Either he must secure a relatively expensive device or onethatwill need frequent replacement.

Many attempts have been made to avoid the necessity of making either ofthese unhappy choices. Most of the devices that have been developed,however, have been so relatively complex that there is little advantagein them from the handpoint of original cost when compared to the pumpprovided with special thrust bearings. In many cases the pump housinghas been provided with a plurality of precision opening passageways andwhat amounts to rotary valve actions that causes them to be even moreexpensive than a pump provided with the special bearings. Many of thesepumps worked well when new but became clogged readily when pumping heavyliquids. This was particularly true if the liquid carried impurities.Some advantage was gained by these pumps in that When they wereoperating properly, they avoided much of the gear canting friction whichcaused the pump to require less power to operate it. If the pumpoperated for a relatively long period of time without involving extramaintenance expense, the savings in power cost would more than offsetany extra original cost. It cannot be said that these complex pumps arewithout merit. It is my opinion, however, that there was considerableroom for improvement as the situation existed prior to my invention.

In view of the foregoing, therefore, it is the principal object of myinvention to provide a means for minimizing wear of internal externalgear pumps that will avoid excessive wear on the external gear.

It is a further object of my invention to provide a means for minimizingwear of internal external gear pumps that avoids excessive wear on thehousing.

It is a further object of my invention to provide a means for minimizingwear of internal external gear pumps that does not over burden the pumpbearings.

It is a still further object of my invention to provide a means forminimizing Wear of internal external gear pumps that is economical tomanufacture, operate and maintain.

These and other objects will be apparent to those skilled in the art.

My invention consists in the construction, arrangement, and combinationof the various parts of the device, whereby the objects contemplated areattained as hereinafter more fully set forth, an specifically pointedout in my cllalinlils, and illustrated in the accompanying drawings, inw 1c Fig. 1 is a perspective view of a pump equipped with means forminimizing wear of internal external gear pumps with broken linesillustrating conduits connected to 1t.

Fig. 2 is an enlarged front elevational view of a pump equipped withmeans for minimizing wear of internal external gear pumps with a portionof the device broken away to illustrate more fully its construction.Broken lines illustrate the arrangement of the chambers at the rear ofthe external gear separated by the divider.

Fig. 2A is a fragmentary front elevational view showing the separatewells 46, 48 in the front cover.

Fig. 3 is an enlarged partial horizontal longitudinal sectional view ofmy pump equipped with means for minimizing wear of internal externalgear pumps taken on the line 33 of Fig. 2.

Fig. 4 is an enlarged partial vertical sectional view of a pump equippedwith means for minimizing wear of internal external gear pumps. Brokenlines illustrate the port location of one of the pressure balancingchambers and the gear face volume by-passes at the forward end of theexternal gear.

Referring to the drawings, I have used the numeral to designate the pumphousing having two ports deslgnated 12 and 14, respectively. Forright-hand or clockwise rotation of the external gear 16 as viewed inFig. 2, port 12 will be the outlet or high pressure port and 14 theinlet or low pressure port. Throughout this discussion the rotation ofthe external gear 16 and the relative pressures at the ports 12 and 14will be assumed as indicated above. The external gear 16 is not unlikesuch gears in conventional pumps except that it is flat on its reardesignated 18. Most conventional gears are relieved on their rearportions to make them lighter. At the inside rear of the housing are apair of semi-circular or half ring form chambers designated 20 and 22and shown most clearly in Fig. 3. These chambers are so positionedrelative to the ports as to cause the perimeters of the ports 12, 14 tointersect the forward portion of the respective chambers 20, 22 formingopenings or passage ways connecting the ports to their respectivechambers.

Liquid under outlet pressure can pass at the point desi nated 24, forexample, from port 12 into chamber 20. Chamber 22 and port 14 areconnected by a passageway designated 26 similar to the one designated24. Separating the chambers 20 and 22 from each other is the verticalpartition or divider 28. The divider 28 is positioned on the axis ofpivot of external gear 16 for any canting action of the latter. For thatreason, just as center seating in an automobile is a smoother ride, itis easier to hold the tolerances between the outer face of the divider28 and the rear 18 of the gear 16. The external gear 16 is secured toany suitable drive shaft such as the one designated 30. Inside theexternal gear is the internal gear 32 which is appropriately journalledon stub shaft 34. The internal gear teeth 36 fit in between the teeth 38of the external gear and the movement of the latter gear drives theformer as a result of their being meshed as in the conventional pump.The internal gear is mounted eccentrically as in the conventional pump.Stub shaft 34 is rigidly secured in the cover plate 40 at the front ofthe pump housing. A gasket 42 creates a liquid tight seal between thecover and the housing whenever the cover plate securing means such ascap screws 44 are tightened. Cover 40 is provided with separate wells 46and 48 which may be of generally segmental or other form, as indicatedin Fig. 2A, and which connect to the housing ports 12 and 14 by means ofthe port extensions 50 and 52. These walls 46, 48 on the forward side ofthe gears are for the puryose of allowing liquid to reach the face ofthe gears 16, 32 as well as the sides. The pump is therefore able topump a large volume of liquid without building up pressure inside thegears 16, 32. The cover 40 also carries the usual crescent (see Fig. 2)to fill the space between the gear teeth 36, 38 on the liquid carryingportion of the rotation of the gears. The cover plate 40 also separatesthe space nearer to the inlet port from the area nearer to the outletport as is clearly shown in Fig. 4.

The clearances between all the moving parts (which is to say betweengear 32 and cover 40; between gears 16, 32; and between the back 18 ofgear 16 and divider 28) provide space for a film of liquid to lubricatethe pump mechanism during operation. This film also means that allsurfaces of the gears 16, 32 are subjected to liquid pressures of somekind. Naturally, the seal, as aforenoted, between the rear 18 of theexternal gear 16 and the divider 28 is not absolutely liquid tight. Theresistance to liquid flow is so great, however, that the pressure dropthat occurs on any liquid that passes from the high to the low pressureside of divider 18 will maintain the pressure differential that permitsthe pump to operate efficiently. This close tolerance fit that causesthe liquid that does pass to the low pressure side to lose its pressurehead is commonly referred to generally and will be also referred to hereas a sliding liquid tight seal. It is a seal against pressure drop onthe pressure side of the pump. In short the pressures existing inchamber 22 at port 14 and well 48 are the same. Likewise the pressuresin chamber 20 at port 12 and in well 46 are also identical to eachother. Consequently, all the space at the left of divider 28 as viewedin Fig. 2 is subjected to outlet or pumping pressures. The space on theright of the divider 28 on the contrary is subjected only to inletpressures. Since the entire left side of the device is subjected topumping pressure While the opposite side is subjected to only inletpressures, there is a force exerted on the moving parts of the pumptending to move them toward the inlet port. Such force has beendemonstrated by field tests to be of little or no significance in termsof the useful life of the pump. Because of this same structure, however,canting forces tending to rock the gears 16, 32 to the left or right asseen in Fig. 3, are materially reduced if not eliminated altogether.Since both the front and the back of one side of the gears 16, 32 aresubjected to pumping pressures, and the area on both the front and theback of said gears that is available for liquid to exert axial pressuresis equal, the total force exerted on the front (left, Fig. 3) tending tomove the external gear rearwardly (right, Fig. 3) exactly equals theopposed forces exerted on the rear of the gears 16, 32. In other words,the wells 46, 48 and the related post extensions 50, 52 expose the samearea at the front of the gears 16, 32 as do the chambers 20, 22 andrelated passageways 24, 26 at the rear thereof, consequently cantingforces are eliminated at least theoretically. Although I have describedthe divider 28 as straight on its forward edge and the external gear asflat backed, it is apparent from the description of the operation of thedevice that such structure is not essential to the operation of thedevice. The sole necessity as to the divider 28 and the external gearback 18 is that they fit each other to form a so-called sliding seal.The rear of the gear could have any symmetrical form, therefore, if thecontour of the leading edge of the divider were contoured to fit therear of the external gear.

In actual field tests the following results were observed. One of thesepumps equipped with the fiatbacked external gear and the divider 28making a slipping fit with the gear was installed in a stone quarrywhere conventional pumps had failed in the space of a few monthsregularly. The pump constructed as herein disclosed operated for aperiod of time that exceeded the usual life of a pump by four or fivetimes. At the end of a period that more than quadrupled the usual pumplife, the pump was completely disassembled and inspected. There weresigns of wear but no indication of imminent failure of the pump. Inanother installation which required frequent replacement of conventionalpumps it was found that by using pumps equipped with the flat backexternal gear and the divider, pump troubles have become a relativelyminor problem. Previously the maintenance of pumps for the installationof my second example was a primary duty of the repair department. Theseexamples are evidence tending to prove two things. They show that thelateral pressures exerted on the gears and referred to above produce noexcessive wear that seriously shortens the useful life of the pump. Theyalso show that by eliminating canting forces exerted on the gears, andthat by placing the seal between the high pressure and low pressuresides of the pump at the canting pivot point of the gears in theconventional pump, the useful life of the pump is multiplied many times.It is also known that the pumps equipped With my invention require lesspower to operate them than do conventional pumps of the same size.

The final advantage of my invention is its relatively simpleconstruction. There are only a relatively few changes that must be madein the design of a conventional type pump to make it a unit embodying myinvention. The pump housing must be cast with the divider and with theports connecting to the chambers. A machining step is required to facethe foremost edge of the divider. The external gear must be made with afiat polished back. Clearly the changes from the conventional pump areslight and will require little or no added expense. Any additional costof machining the divider will be compensated for by relative ease ofmachining it as compared to the machining required for the inside rearperiphery of the conventional housing. In practice it has been foundthat these pumps can compete very favorably with conventional pumps asto price. Clearly I have invented a device that achieves the objects ofmy invention.

Some changes may be made in the construction and arrangement of my meansfor minimizing wear of internalexternal gear pumps without departingfrom the real spirit and purpose of my invention, and it is my intentionto cover by my claims, any modified forms of structure or use ofmechanical equivalents which may be reasonably included within theirscope.

I claim:

1. In an internal-external gear type pump having a pumping chamber andmeshing, eccentrically positioned exterior and interior gears thereinand an inlet port and an outlet port communicating with said chamberwith means in the housing adjacent the face of said gears forrestricting inlet pressures to those face portions of the external gearthat are nearer to said inlet port and for restricting outlet pressuresto those face portions of the external gear that are nearer to saidoutlet port; said pump characterized by a rear chamber extension formedon the back side of said gears opposite to said face of said gears, theentire back side of said external gear being closed, a divider formed insaid chamber extension and fixed to the back of said pump housing andextending to and forming a liquid tight sliding seal with the back sideof said external gear; said divider separating said chamber extensionalong a line that separates those portions of the back of said externalgear that are nearer to said inlet port from those portions of the backof said gear that are nearer to the outlet port; means for connectingthe portion of said chamber extension Which is nearer to said inlet portto inlet pressures, and means for connecting the portion of said chamberextension which is nearer to said outlet port to discharge pressures;whereby axial pressures exerted on the front and back portions of theexternal gear nearer to said outlet port are discharge pressures; andwhereby all axial pressures exerted on the front and back of saidportions of said external gear nearer to said inlet port are inletpressures.

2. In an internal-external gear pump having a housing providing asubstantially circular pumping chamber having front and rear walls and afluid inlet and a fluid outlet port communicating with said chamber atremote peripheral points, the back of said housing providing twoseparate rear enlargements of said pumping chamber, one enlargementbeing nearer the inlet port and in open communication therewith and theother enlargement being nearer the outlet port and in open communicationtherewith, a forwardly extending divider partition extending betweenopposite peripheral portions of said chamber and carried by said casingback, said divider partition separating said rear chamber enlargements,an external gear journalled in said pumping chamber adjacent the backthereof,

the entire back face of said external gear being closed and bearingagainst said outer end of said divider partition in the plane of theaxis of said gear, an internal gear smaller than said external gear andeccentrically journalled in said housing with respect to said externalgear and adjacent the front housing wall, the front housing wallproviding two separate front chamber enlargements, one of the latterbeing nearer the inlet port and in open communication therewith and theother front chamber enlargement being nearer the outlet port and in opencommunication with the latter, each of said front chamber enlargementshaving a gear-facing area approximating that of said rear chamberenlargements, and means connecting one of said gears to a source ofpower.

References (Iited in the file of this patent UNITED STATES PATENTS1,636,259 Sweeney July 19, 1927 1,732,871 Wilsey Oct. 22, 1929 1,768,818Bock July 1, 1930 1,970,146 Hill Aug. 14, 1934 2,373,368 Witchger Apr.10, 1945 2,531,808 Eames Nov. 28, 1950

